Ultrasonic diagnostic imaging systems are in widespread use for performing ultrasonic imaging and measurements. For example, cardiologists, radiologists, and obstetricians use ultrasonic diagnostic imaging systems to examine the heart, various abdominal organs, or a developing fetus, respectively. In general, imaging information is obtained by these systems by placing an ultrasonic probe against a transmission agent such as a liquid gel and the skin of a patient, and actuating an ultrasonic transducer located within the probe to transmit ultrasonic energy through the skin and into the body of the patient. In response to the transmission of ultrasonic energy into the body, ultrasonic echoes emanate from the interior structure of the body. The returning acoustic echoes are converted into electrical signals by the transducer in the probe, which are transferred to the diagnostic system by a cable coupling the diagnostic system to the probe.
Acoustic transducers commonly used in ultrasonic diagnostic probes are often comprised of an array of individual piezoelectric elements. These elements are usually formed from a piezoelectric material by the following a number of meticulous manufacturing steps. In one common method, a piezoelectric transducer array is formed by bonding a single block of piezoelectric material to a backing member that provides acoustic attenuation. The single block is then laterally subdivided by cutting or dicing the material to form the rectangular elements of the array. Electrical contact pads are formed on the individual elements using various metallization processes to permit electrical conductors to be coupled to the individual elements of the array. The electrical conductors are then coupled to the contact pads by a variety of electrical joining methods, including soldering, spot-welding, or by adhesively bonding the conductor to the contact pad.
Although current methods such as the foregoing are generally adequate to form acoustic transducer arrays having up to a few hundred elements, larger arrays of transducer elements having smaller element sizes are not as easily formed using these approaches. Consequently, various techniques used in the fabrication of silicon microelectronic devices have been adapted to form ultrasonic transducer elements, in part because these techniques generally permit the repetitive fabrication of small structures in intricate detail.
An example of a device that may be formed using semiconductor fabrication methods is a micro-machined or micro-fabricated ultrasonic transducer (MUT). The MUT has several significant advantages over conventional piezoelectric ultrasonic transducers. For example, the structure of the MUT generally offers more flexibility in terms of optimization parameters than is typically available in conventional piezoelectric devices. Further, the MUT may be conveniently formed on a semiconductor substrate using various semiconductor fabrication methods, which advantageously permits the formation of relatively large numbers of transducers. The formation of numerous transducers may then be integrated into providing large transducer arrays. Additionally, interconnections between MUTs in arrays and the electronic devices external to the arrays may also be conveniently formed during the fabrication process. MUTs may be operated capacitively, and are commonly referred to as cMUTs, as shown in U.S. Pat. No. 5,894,452, which is incorporated by reference herein in its entirety. Alternatively, piezoelectric materials may be used in fabrication of MUTs, which are commonly referred to as pMUTs, as shown in U.S. Pat. No. 6,049,158, which is incorporated by reference herein in its entirety. Accordingly, MUTs have increasingly become an attractive alternative to conventional piezoelectric ultrasonic transducers in ultrasound systems.
Furthermore, some ultrasound devices available today utilize multiple, individual transducer elements supported by quilt-like substrates. See U.S. Pat. App. Pub. No. 2006/0241522, which is incorporated by reference herein in its entirety. Such materials in these devices may not provide adequate ultrasound transmission efficiency or satisfactory imaging resolution.
There is a need for instrumentation and procedures capable of obtaining ultrasound images and other types of medical data information using a coordinated interconnected network of micro-fabricated elements that can be manufactured efficiently and in a cost effective manner.